You could argue that the treaty of versailles was the primary cause of war, since it caused germany to have hyperinflation, due to the reparations put in place for them to pay for the damages caused in ww1, which led to the weimar republic to print more money to deal with the payments, just increasing the currency’s inflation. the treaty of versailles angered many people, including hitler, which thought the weimar republic was stabbing germany behind their back (dolchstoss theory) by accepting those outrageous terms
Hitler would just take countries and the ALLIES were fine with it until he invaded poland. They said it would cause war. So, Hitler invaded Poland and the UK and France declared war on Germany
